The present invention relates to an apparatus for obtaining a small quantity of material which is representative of the average of some large amount of the material, and in particular to an apparatus for cyclically obtaining and collecting small samples of heterogeneous granular material from a bulk of such material as it is transported past a sampling station.
In the manufacture or mining of heterogeneous granular materials, such as cement clinker, crushed ore, coal, phosphate rock and the like, which are composed of small lumps or particles differing in diameter and composition, the materials are often transported from one point to another by, for example, a belt-type conveyor. To determine the properties of these materials, it is common practice to take small samples therefrom and to analyze the samples.
Sampling may consist of periodically taking portions from a stream of material as it is transported past a sampling station. A number of samples obtained from different parts of the flow of bulk material are then combined to build a composite sample which is representative of the average of the total material flow. The contents of the composite sample are thoroughly mixed and perhaps crushed, whereafter a sample is taken therefrom of a size customary for analyzing.
The different sizes of granules of the heterogeneous bulk material to be sampled tend to segreate when the material is transported on a conveyor. On account of this segregation, some samplers have been designed to cut samples periodically from a stream of material discharging from an end of the conveyor by intermittent transverse movements across the stream. The length of these cuts depends upon the width of the stream of material, and therefore the size of every sample will be comparatively large if the stream is wide, as is usually the case with products transported in bulk. The composite sample will thus be undesirably large, and the greater accuracy which might be expected to result from a large total sample is not in fact attained due to the need to subsequently split the large sample to obtain a small sample suitable for analysis.
Another sampling technique is disclosed in U.S. Pat. No. 2,654,249. In the apparatus therein disclosed, a sample collecting tube is rotated through material on a conveyor in a direction against the movement of the material and about an axis extending across the material parallel to the major plane thereof and transversely of the direction of material flow. Because of the particular orientation of the axis of rotation, the tube moves through the material in a plane perpendicular to the major plane of the material and extending along its direction of movement, with the result that there is no component of movement of the tube transversely of the material, whereby samples of transversely segregated portions of the material are not obtained. In addition, because the tube moves against the direction of material movement, there is disruption of the material and scattering of the same off of the conveyor. After collecting the sample, the tube is rotated to an upper portion to cause the sample to fall through the tube for collection.
In another type of apparatus a scoop on an end of an arm is rotated through material on a conveyor and about an axis extending across the material parallel to the major plane thereof and transversely of its direction of movement. In this case, however, the scoop is moved through the material along its direction of flow, whereby disruption and scattering of the material is minimized. After collecting a sample, the scoop is then rotated to a position above the conveyor whereat movement thereof is abruptly stopped. This causes the sample of material to move out of the scoop, as a result of inertia, for collection in a suitable container positioned in its fall line.
The container, of course, must be positioned out of the plane of rotation of the scoop in order to avoid interference with either. The speed of the scoop approximately equals the speed of the material on the conveyor, and for conveyor speeds in excess of about 300 feet per minute such an arrangement is satisfactory since the inertia of the material is then sufficient to carry the material beyond the plane of rotation of the scoop and into the container. For conveyor speeds of less than 300 feet per minute, however, the inertia of the material is usually insufficient to carry it out of the plane of rotation of the scoop, with the result that at least some of the material falls back onto the conveyor.
In order to collect samples from slow moving conveyors, in a sampler somewhat similar to that just above described the arm supporting the scoop has a passage through which the material may travel for collection without being thrown out of the scoop. This technique is satisfactory for conveyor speeds of 200 feet per minute or less, since inertia does not then tend to move the material out of the scoop when the scoop is stopped. With conveyor speeds in excess of 200 feet per minute, however, at least some of the material is thrown out of the scoop as the same is stopped, whereby a portion if not all of the sample is lost. Consequently, neither type of apparatus is suitable for use with all conveyor speeds which might reasonably be encountered, and neither is entirely satisfactory where the speed is in the range of 200 to 300 feet per minute. In addition, since the scoop in each apparatus moves in a plane perpendicular to the major plane of the material and along the direction of movement thereof, there is no transverse movement of the scoop through the material and transversely segregated portions of the material are not sampled.